In the mid-1950s the head of the Dutch Provincial Psychiatric Service of Groningen, Dr H. Kuipers, became involved in a fierce dispute with Mr J.J. Zuidema, the headmaster of the local school for children with mental disabilities. Both the psychiatrist and the headmaster claimed authority over the testing of children's intelligence as part of the school's admission procedure. When the dispute escalated the headmaster withdrew and the tests were suspended until an alternative solution was found. The present article analyses this conflict over the demarcation of expertise in terms of a broader debate occurring in the first half of the twentieth century between advocates of pedagogisation and medicalisation. At the time, establishing the intelligence of children had originally been a task for physicians; however, on the basis of a developing pedagogical awareness the procedure became a pedagogical practice during the second half of the century. This development is in accordance with the concept of pedagogisation. In contrast, in the dispute described in this paper, the psychiatrist attempted to expand his influence by controlling the most important aspect of the admission procedure, a move that is in accord with the concept of medicalisation. While the struggle in Groningen can thus be understood as a clash between these two processes of medicalisation and pedagogisation, ultimately neither the psychiatrist nor the headmaster triumphed and it was a third party, the school psychologist, who eventually became responsible for administering the intelligence test. This sub-discipline of psychology was strongly influenced by pedagogical concepts. Testing intelligence became subject of the debate between academic pedagogues and psychologists. (Contains 2 figures, 1 table, and 81 footnotes.)